Stretch laminates are well known in the art. It has long been known in the field of disposable absorbent articles that it is desirable to construct absorptive devices, such as disposable diapers with fasteners, pull-on diapers, training pants, sanitary napkins, pantiliners, incontinence briefs, and the like, with stretch laminates to improve the ease of motion and maintenance of a sustained fit. Furthermore, stretch laminates allow the diaper to accommodate a range of different sized wearers. A diaper may have stretch laminates in a number of its article elements including the waist band, leg cuffs, side panels, elasticized topsheets, backsheet, ears, outercover, and fastening system.
During application, a diaper generally may be stretched and elongated longitudinally and/or laterally from its initial substantially compacted and untensioned state. Upon release of the elongating tension, the diaper often contracts, constricts, and/or folds before it can be successfully applied to or adjusted on a wearer. In traditional taped diapers, the stretch laminates, which may be present in a leg cuff, may require elongation prior to application onto a wearer. However, if a continuous force is not maintained, the stretch laminates within the leg cuff may cause the diaper to retract quickly. Generally, a caregiver needs to apply a continuous elongating force to the diaper while at the same time positioning the diaper onto the wearer and tending to the wearer who may be uncooperative (e.g., crying, fussing, moving, resisting, etc.) during the diapering process. These multiple simultaneous requirements can lead to frustration for the caregiver. The multiple simultaneous requirements may result in the diaper being positioned improperly on the wearer.
Similarly, in pant-type articles, the stretch laminates, which may be present in a waist feature, side panel, leg band or outer cover, may require elongation so as to enlarge the waist opening from an initial constrictive and untensioned state. A continuous force may need to be applied during the application process, generally by a caregiver or wearer, to counteract the rapid retraction of the stretch laminates that would be experienced otherwise. Leg openings in pants-type articles commonly incorporate stretch laminates and may also tend to retract quickly thereby increasing the difficulty of pulling the article up to the desired location on the wearer's lower torso. Applying a continuous force to maintain an enlarged waist opening may be difficult for young children who lack the hand strength and dexterity to apply the continuous force while simultaneously pulling on the pant. Likewise, elderly individuals may also lack the necessary hand strength and dexterity to apply a continuous force while simultaneously pulling on an incontinence article.
Furthermore, recent diaper advancements have focused on the acceptance and storage of feces. In conventional diaper designs, feces remain between the diaper's topsheet and the wearer's skin. As a result, the wearer experiences excessive soiling, irritation, and the potential of leakage generally around the leg cuff. Advances in diaper design include the use of an apertured elasticized topsheet to isolate feces away from the wearer's skin thus preventing leakage and irritation. The apertured elasticized topsheet forms a void between the elasticized topsheet and the underlying diaper structure. A stretch laminate generally is associated with the elasticized topsheet to aid in keeping the elasticized topsheet substantially in contact with the wearer's skin. Furthermore, the stretch laminate aids in keeping the aperture positioned so that the underlying diaper structure may receive the fecal insult. Examples of elasticized topsheets may be found in U.S. Pub. Nos. 2005-0273071, 2005-0171499, 2007-0191806, 2004-0162538, and 2005-0095942.
While elasticized topsheets are conceptually advantageous, diapers with elasticized topsheets comprising conventional elastomers are often difficult to apply. Application of the diaper requires a caregiver to stretch the diaper so that it is in a substantially planar position. Upon release, the stretch laminate contracts at a rate that makes it difficult for the caregiver to position the diaper correctly onto the wearer. This “snap-back” of the elasticized topsheet may increase the difficulty of applying the diaper to the wearer. If the diaper is difficult to apply, there may be a tendency for mispositioning the aperture, which may result in fecal deposit on the elasticized topsheet rather than through the aperture. Mispositioning of the aperture can destroy the benefit of isolating feces from the wearer's skin. Examples of diapers comprising an elasticized topsheet having an aperture have been disclosed in U.S. Pat. No. 4,892,536, issued to Des Marais et al. and U.S. Pat. No. 4,990,147 issued to Freeland.
Thus, there is a need for an absorbent product comprising a stretch laminate that retracts slowly upon being released from a stretched state, thus facilitating application and positioning of the product correctly onto the wearer.
One problem that exists in filling the need for a stretch laminate that retracts slowly upon release from a stretched state is that stretch laminates are an amalgam of materials. Stretch laminates generally may include an elastic member and a relatively inelastic substrate. The elastic member and the substrate may be joined by bonding techniques known in the art such as by an adhesive. It is the combination of these materials as a laminate that must result in the slow recovery. Furthermore, the formation technique can affect the recovery characteristics of the resultant stretch laminate. For example, a stretch bonded laminate involves joining a strained elastic member to a substantially inelastic substrate. Upon release of the strain force, the elastic member retracts and may gather the substrate. The initial strain of the elastic member can impact the extendibility and the recovery characteristic of the stretch laminate. The construction and basis weight of the substrate may also impact the recovery characteristic of the stretch laminate.
Another problem that exists in filling the need for a slow recovery stretch laminate is that during the manufacture of said stretch laminate, the elastic member should be strained relatively uniformly in order for the laminate to have consistent properties and thereby provide reliable performance for the end user. Additionally, for economic reasons, it is advantageous to fabricate the stretch laminate in a high line speed continuous process, which in turn further complicates the manufacture of a slow recovery stretch laminate with reliable performance. This additional complication is primarily a result of the higher characteristic strain rates the elastic member experiences at high line speeds. For a given stretch lamination process and operating temperature, as line speed is increased, the strain rate increases, and higher strain rates more readily give rise to stability problems in the stretching process.